John Barrow: Some Generalities About Generality

John D. Barrow - via commons
On 1 December 2014 I had the pleasure of attending a lecture by John David Barrow at the "Enriques" Department of Mathematics in Milano. Very kind person, when I approached him to be able to shake his hand and take a picture of him, he granted me both honors with great simplicity. Unfortunately that photo has now been lost among smartphone changes, perhaps kept in some hard disk stored somewhere, nor did I publish it on one of my social networks, but I still wanted to pay homage to it by offering you the abstract of an article from 2015, the fifth chapter of the book The Philosophy of Cosmology (arXiv):
We survey a variety of cosmological problems where the issue of generality has arisen. This is aimed at providing a wider context for many claims and deductions made when philosophers of science choose cosmological problems for investigation. We show how simple counting arguments can be used to characterise parts of the general solution of Einstein's equations when various matter fields are present and with different spatial topologies. Applications are described to the problem of singularities, static cosmological models, cosmic no hair theorems, the late-time isotropisation of cosmological models, and the number of parameters needed to describe a general astronomical universe.

The flying Batman

Comics' authors, and more generally those who write about fiction (but not only them), are the modern Scheherazade of One Thousand and One Nights. This comparison is very fitting for Detective Comics #1027 which celebrates at the same time #27, where Bob Kane and Bill Finger's Batman made his debut, and the 1001th issue of the magazine dedicated to the Caped Crusader, so you understand the initial comparison.
I'm not here, though, to write you why Detective Comics's 1001 releases with Batman (if you want to, follow note(1)), but to seize the opportunity and talk about Batman's physics.

Robot stories

The comic transposition of Isaac Asimov's I, robot created by Raul Cuadrado is reminiscent of the first flash animations of a decade ago, a bit like the style of Carlos Meglia, famous in particular for Cybersix. Made on a horizontal rather than vertical page structure reminiscent of newspaper strip stories, the comic book I, robot is a quick and intelligent reading, with a slightly retro style thanks to the duotone, true to Asimov's spirit.

The obscure Planet Nine

Planet Nine is an hypothetical plante in Our Souls System. Its existence is inferred by the orbital data of a group of extreme trans-Neptunian objects, that seemed influenced by the presence of an undiscovered planet, or something else. Recently Amir Siraj and Abraham Loeb proposed a new hypothesys: Planet Nine could be a little black hole, about five times more massive than Earth with the dimension of an orange:
Planet Nine has been proposed to potentially be a black hole in the outer solar system. We investigate the accretion flares that would result from impacts of small Oort cloud objects, and find that the upcoming LSST observing program will be able to either rule out or confirm Planet Nine as a black hole within a year. We also find that LSST could rule out or confirm the existence of trapped planet-mass black holes out to the edge of the Oort cloud, indirectly probing the dark matter fraction in subsolar mass black holes and potentially improving upon current limits by orders of magnitude.
Siraj, A., & Loeb, A. (2020). Searching for Black Holes in the Outer Solar System with LSST. ApJL 898 L4 arXiv:2005.12280. doi:10.3847/2041-8213/aba119 (arXiv).

The distance from the Moon

The method currently used to evaluate the distance from the Moon dates back to 1962, when a team from MIT (Massachusetts Institute of Technology) in collaboration with soviet astronomers from the Crimean Astrophysical Observatory carried out an experiment to measure the round-trip time of a laser pulse reflected on the surface of the Moon. The evolution of this experiment was completed thanks to the Apollo missions of 1969, when the astronauts placed reflective mirrors on the lunar surface in order to improve the accuracy of the measurement. Lasers traveling to the Moon involve multiple structures and are part of the Lunar Laser Ranging.
The distance measurement from this project is 384402 km with an error of 1.1 millimeters(1), which in terms of light time corresponds to just under 1.3 seconds.
The pre-laser method is also inspired by the same principle: in 1957 the US Naval Research Laboratory sent 2 μs radar pulses from a radio antenna with a diameter of about 15 meters. After the echo produced by the waves on the surface of the Moon, the experiment detected the return signal and measured the delay time, from which to derive the distance from our satellite. Unfortunately, this experiment was subject to an excessively high error with respect to the signal and therefore the result produced was not considered reliable(2).
The experiment was repeated the following year, in 1958, by the Royal Radar Establishment in Great Britain. In that case, radar pulses of 5 μs were sent with a maximum power of 2 megawatts and a frequency of 260 pulses per second(3).

Human: the man of the future

500,000 years and more in the future. Disused satellites and space debris orbit around the Earth. Among these there is a structure that resembles a space station. Suddenly a module detaches and crashes onto the planet. After the explosion, we follow an animal that, from the top of a cliff, spreads its wings and flies to the impact site. From the relatively distant readers' point of view, the flying shadow could be a pterodactyl and the Earth we see, in reality, that of prehistory: even the vegetation and the gigantism of the environment would seem to suggest it. Instead, when we get closer to the impact site, the figure becomes more defined: it is a kind of monkey with wings.
The guides in the exploration of this regressed world of the future are Diego Agrimbau and Lucas Varela and they use a robot, Alpha, as their guide. His job is to assist the terrestrial scientist Robert who, together with his wife June, devised a complex plan to repopulate the Earth with homo sapiens. Robert, in fact, predicting the fate of extinction of human beings, has decided to freeze himself and his wife while waiting for the planet to recover from the ecological disasters left on its surface by the passage of the human race.

Rocks from space

via commons
Our solar system is crossed by a lot of rocks like comets and meteorites. Following the panspermia hypotesis, these cosmic objects could be at the origin of life-as-we-know. And two paper recently published seems confirmed it.
Comet 21P/Giacomini-Zinner belongs to the cometary family of Jupiter, with an orbital period of about 6.6 years. Discovered on the 20th decembre 1900 by Michel Giacobini, it could be the origin of the Draconids meteor shower. In July 2005 a japanese team of astronomers decided to observe 21P using the Comics instrument (Cooled Mid-Infrared Camera and Spectrometer) mounted on the Subaru telescope. Now they have concluded the examination of data, detecting an unidentified infrared emission, as well as thermal emissions generated by the silicate and carbon grains, which is probably due to complex organic molecules.
Ootsubo, T., Kawakita, H., Shinnaka, Y., Watanabe, J. I., & Honda, M. (2020). Unidentified infrared emission features in mid-infrared spectrum of comet 21P/Giacobini-Zinner. Icarus, 338, 113450. doi:10.1016/j.icarus.2019.113450
In the meanwhile another japanese team studied a couple of meteorites falled on Earth: Nwa 801, recovered in 2001 in Morocco, and Murchison, fallen in Australia in 1969.
Also in these cases the results are very interesting: the team, indeed, find some sugars essential for life: ribose and other biotic sugars, including arabinose and xylose. In particular the ribose is an essential component of ribonucleic acid, commonly known as Rna, a molecule of fundamental importance for life. This nucleic acid, in fact, performs the delicate function of copying the genetic instructions contained in the DNA molecule (deoxyribonucleic acid) to deliver them to the molecular factories inside the cell, called ribosomes, where proteins are synthesized.
Furukawa, Y., Chikaraishi, Y., Ohkouchi, N., Ogawa, N. O., Glavin, D. P., Dworkin, J. P., ... & Nakamura, T. (2019). Extraterrestrial ribose and other sugars in primitive meteorites. Proceedings of the National Academy of Sciences, 116(49), 24440-24445. doi:10.1073/pnas.1907169116

A laser particle accelerator

Particle accelerators are usually associated with large national facilities. Because photons are able to impart momentum to electrons, there are also efforts to develop laser-based particle accelerators. Sapra et al. developed an integrated particle accelerator using photonic inverse design methods to optimize the interaction between the light and the electrons. They show that an additional kick of around 0.9 kilo–electron volts (keV) can be given to a bunch of 80-keV electrons along just 30 micrometers of a specially designed channel. Such miniaturized dielectric laser accelerators could open up particle physics to a number of scientific disciplines.
Sapra, N. V., Yang, K. Y., Vercruysse, D., Leedle, K. J., Black, D. S., England, R. J., ... & Byer, R. L. (2020). On-chip integrated laser-driven particle accelerator. Science, 367(6473), 79-83. doi:10.1126/science.aay5734